1. Field of the Invention
The invention relates to an antenna structure and, more particularly, to an antenna structure which is directly printed on a circuit board.
2. Description of the Related Art
Because of the demand of the market, the sizes of electronic devices such as notebook computers or mobile phones become smaller and smaller. If the sizes of antennas in the electronic devices also decrease correspondingly, it helps the electronic devices to be small.
If an antenna used in a 2.4 GHz band is designed as one-quarter of the wavelength, the volume of the antenna is about 720 mm3. As a result, the antenna is difficult to be applied to a small electronic device. An antenna also can be made of multilayer ceramic material, and then the antenna can have a small size via the high dielectric coefficient of the ceramic material. However, the cost of the antennas made of the ceramic material is high, and the radiation efficiency is low (about fifty percent). If the antenna made of the multilayer ceramic material is disposed in a little casing, the working bandwidth decreases, and then the communication quality of part of the band decreases.